Fall knees is a phrase that does not have an antonym. It is a common idiomatic expression that refers to the loss of strength or courage in a person, which causes them to kneel down in submission or defeat. However, there are many other antonyms that can be used to describe related concepts such as strength, courage, and perseverance. Some examples include resilience, fortitude, determination, persistence, and tenacity. These words describe the ability to overcome obstacles, stay focused on goals, and push through difficult times without giving up or losing heart. Despite the fact that there is no direct antonym for "fall knees," there are many alternatives that can be used to convey similar sentiments.